net/smc: rkey processing for a new link as SMC server

Part of SMC server new link establishment is the exchange of rkeys for
used buffers.
Loop over all used RMB buffers and send ADD_LINK_CONTINUE LLC messages
to the peer.

Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Reviewed-by: Ursula Braun <ubraun@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>